This invention relates to chemical-mechanical polishing methods.
Chemical-mechanical polishing (CMP), also known as chemical-mechanical planarization, is widely used in a variety of industries, including the semiconductor processing industry. CMP can remove unwanted material from a substrate, planarize a substrate, and/or create a desired finish on a substrate. All of such intentions may be generically termed xe2x80x9cpolishing.xe2x80x9d Generally, the technology involves pressing some sort of solid abrasive material against the substrate to accomplish the polishing and/or planarization. The solid abrasive material may be applied in a CMP slurry of such material and liquid carriers and/or chemically active components as desired. Alternatively, abrasive material may be carried within a polishing pad. Still other techniques are encompassed within the technology.
One common by product of CMP is that abrasive material residues often remain on the substrate. In some applications, residual abrasive material can negatively influence subsequent processing and/or result in defective products. Accordingly, a variety of approaches have been attempted to resolve the problem of residual abrasive material.
One conventional approach is to use hydrofluoric acid-based chemistries to undercut particles attached to a silicon oxide substrate. A problem with hydrofluoric acid-based chemistries is that microscratches formed in the substrate as a result of CMP may be aggravated in the acidic conditions. Further, insoluble fluoride compounds may be formed from reactions of hydrofluoric acid with the abrasive material.
Another conventional approach includes application of ammonium hydroxide or tetramethylammonium hydroxide (TMAH) to disperse residual abrasive material. At a high pH, a silicon oxide surface and most abrasive material particles, including ceria, alumina, and silica exhibit a negative surface charge. Such charge characteristics provide electrostatic repulsion. Experimentally, such a method has produced limited benefits and appears to work much better for aluminum oxide particles in comparison to cerium oxide particles.
Still another conventional technique involves etching and/or dissolution of abrasive particles. For cerium oxide particles, such may be accomplished with the application of a mixture of hydrogen peroxide and sulfuric acid. While this method exhibits some effectiveness experimentally, it is incompatible with any surface structures featuring exposed metal.
Accordingly, it is desired to provide a new method for removing CMP residual abrasive material from a substrate.
In accordance with an aspect of the invention, a chemical-mechanical polishing (CMP) method includes applying a solid abrasive material to a substrate, polishing the substrate, flocculating at least a portion of the abrasive material, and removing at least a majority portion of the flocculated portion from the substrate. Such a method can include polishing with a CMP slurry or polishing pad. It may further include applying a surfactant-comprising material to the substrate to assist in effectuating flocculation of the abrasive material. Such surfactant so comprising material may be cationic which includes, for example, a quaternary ammonium substituted salt. Also, for example, the surfactant-comprising material may be applied during polishing, brush scrubbing, pressure spraying, or buffing.